Measurement Of Pupil Displacement And Eyclotorsion Using Iris Registration In LASIK

After more than a decade the constant improvement of the excimer laser corneal refractive surgery,the continuous improvement of the excimer laser,advantage of its therapeutic effect with high safety, predictability and faster visual recovery,has been accepted by an increasing number of patients this is because the aberration of the eye surgery increases,to reduce the imaging of the retina.With the deepening of the understanding，“customized ablation "for corneal and refractive status came into being.Currently individualized clinical customized ablation mainly:wavefront aberration supported customized ablation, corneal topography guided customized ablation,adjust the Q value of the individual ablation etc. Wavefront aberration supported customized ablation reduce higher-order aberrations, the safety and effectiveness of the correction of myopia and myopic astigmatism has been confirmed.Wavefront aberration guided laser cutting of eye position, is put forward higher requirements to the rotation of the eye,in particular, the rotation of the eye a higher demand,in order to improve the quality of postoperative visual,to carry out the wavefront aberration guided individualized ablation, there are many issues to be research,pupil diameter changing and body position changing can cause the pupil centroid shift and ocular eyclotorsion preoperatively and intraoperatively, this may affect the correction effect,and domestic wavefront aberration guide the ablation surgery research is not very comprehensive. Iris positioning technology is different states iris texture image data by the wavefront aberration measurement systems and iris recognition system records,the eyes can not only verify the measurement of wavefront analyzer eye iris and treatment is the same eyes,and phase junction compensation the offset of the center of the pupil in different states with active eye tracking system(X axis and Yaxis locate)and eyeball rotation angle (rotational positioning),even serious center shift and eye surgery rotation repositioning,thus more accurately determine the center of the positioning of the laser cutting point.lris positioning technology,first use of iris outer edge as to determine the center(the outer edge of the iris deemed circumference,the circumference center that iris outer edge of the center)reference(pupil in all the time to change,iris outer edge but not,its center does not change),checked by comparison wavefront aberration and the laser cutting of the shift of the center of the pupil and iris positioning system calculating an adjustment of the shift of this part,ultimately improve cutting accuracy,minimize the occurrence of higher-order aberrations.Surgery good iris recognition technology,make surgery eccentric cutting induced coma increased by a considerable degree of impaired,iris recognition is also very important to the tracking and location of eye rotation.Especially for patients with high astigmatism,if there is no iris positioning and rotation tracking will cause a large cutting errors,that affect postoperative visual quality.In this study, iris recognition software,Pupil shift and rotate the eye research,To analyze the pupil centroid shift and ocular cyclotorsion caused by pupil diameter changing and body position changing in LASIK, The wavefront aberration guided LASIK surgery to achieve perfect results.MethodsFrom July2011to September2012,450cases840eyes with refractive error received preoperative examination in the excimer laser treatment center of our hospital.Men260cases450eyes,women190cases390eyes, Right eye420eyes,left eye420eyes.Aged18to39years old, on average (23.0±4.7) years.We analyzed and cylinder and spherical equivalent refractions before laser in situ keratomileusis with Zywave aberrometer and OrbscanII, by statistic software.Zywave wavefront aberrometer was performed preoperatively and the iris recognition software of the Technolas217Z100excimer laser was performed intraoperatively on840eyes to measure the distance of the pupil centroid shift and the degrees of ocular cyclotorsion caused by the change of pupil diameter and body position.The were analyzed by SPSS17.0statistical software with paired-test, P<0.05is considered as the standard of significant difference.Results1Pupil center shift distance and the rotation angle of the eye caused by the change of pupil diameter1.1pupil center shift distance840eyes preoperative Zywave wavefront aberration check, Measuring pupil bulk large to6.0-7.5mm by4.5-5.5mm, The pupil center the average horizontal direction (x-axis) shift (55.81±56.25) μm、the range isO-244μm, The average vertical direction (Y axis) shift (74.01±53.75) μm、the range is5-246μm, The mean vector direction of the shift (99.65±67.32) μm、the range isl2-260μm。 Between the shift of the center of the pupil of the right eye and the left eye was no significant difference (P>0.05)(Table1).There are right eye pupil center shift to each quadrant, the mosts are the down nasal quadrant shift(36.67%)。 Followed by inferior temporal quadrant(30.00%), the up nasal quadrant(23.33%), The superior temporal quadrant(10.00%)。 There are also left eye pupil center shift to each quadrant, the mosts are the down nasal quadrant shift(36.67%)。 Followed by inferior temporal quadrant(30.00%), the up nasal quadrant(23.33%), The superior temporal quadrant(10.00%).1.2rotation angle of the eyePupil diameter changes caused by eye rotation an average of1.15°±0.98°,the range isO-4.34°Internal rotation of the right eye, accounting for53.13%, external rotation accounted for37.50%, no rotation accounted for9.37%; Internal rotation in the left eye, accounting for48.49%, external rotation accounted for45.45%, no rotation accounted for6.06%。Right eye and the left eye was not statistically significant (P>0.05).2The postural changes caused by pupil center shift and rotation angle of the eye2.1pupil center shift distanceThe840eyes wavefront wavefront aberration guided LASIK treatment, check from sitting to supine position surgery, postural changes, Iris recognition software measurement pupil center horizontal direction (X-axis) shift (59.23±51.38) μm、 the range isO-244μm; The average vertical direction (Y axis) shift (73.12±56.08) μm、 the range is1-250μm。Between the shift of the center of the pupil of the right eye and the left eye was no significant difference (P>0.05)(Table2)。There are right eye pupil center shift to each quadrant, the mosts are the superior temporal quadrant (35.48%), followed by the up nasal quadrant(29.04%), inferior temporal quadrant (22.58%),the down nasal quadrant (12.90%).There are also left eye pupil center shift to each quadrant, the mosts are the superior temporal quadrant(35.48%), followed by the up nasal quadrant(29.04%), inferior temporal quadrant (22.58%),the down nasal quadrant (12.90%).Left and right eyes are the maximum of the superior temporal quadrant.2.2rotation angle of the eyePostural changes caused by the average eye rotation3.81°±2.750°, the range isO°～9.9°,27(eyes) eye rotation more than5°(33.33%)。 Right eye more than5°rotation accounted for35.71%, internal rotation accounted for34.38%, external rotation accounted for62.50%, no rotation accounted for3.12%。Left eye more than5°rotation accounted for29.63%, internal rotation accounted for48.28%, external rotation accounted for44.82%, no rotation accounted for6.90%。 Right eye and the left eye eye rotation difference between the degree was not statistically significant (P>0.05). ConclusionsPupil diameter changing and body position changing can cause the pupil centroid shift and ocular eyclotorsion preoperatively and intraoperatively. The technology of iris recognition can be used to measure and regulate the displacement distance and the ocular eyclotorsion degrees exactly.